In the field of graphic arts, an image forming system showing photographic characteristics of high contrast (10 or more of gamma) is required for attaining good reproduction of a continuous gradation image formed by a halftone image or good reproduction of line drawings.
For such a purpose, hitherto, a special developing solution called lith-developing solution has been used. The lith-developing solution contains only hydroquinone as a developing agent, wherein free sulfite ion concentration is kept at a very low value by using, as a preservative, sulfite in a state of an adduct of formaldehyde so that infectious developability thereof is not damaged. Therefore, the lith-developing solution has a serious fault that it cannot be preserved over 3 days, because it is very easily oxidized by the air.
As a process for obtaining the photographic characteristics of superhard tone using a stable developing solution, there is a process using hydrazine derivatives described in U.S. Pat. Nos. 4,224,401, 4,168,977, 4,166,742, 4,311,781, 4,272,606, 4,221,857 and 4,243,739. According to this process, photographic characteristics of high contrast and high sensitivity are obtained and stability of the developing solution to oxidation by the air is remarkably improved as compared with the lith-developing solution, because sulfite of high concentration can be added to the developing solution. However, this process using hydrazines has a problem that it requires a comparatively long developing time for obtaining the desired photographic characteristics of high contrast and high sensitivity. For example, among the examples of the above-described U.S. patents, a developing time of 1 minute to 3 minutes is usually used, and there is a tendency to require a longer developing time with lowering of the pH value of the developing solution.
In the field of graphic arts, it is very important to solve the above-described problem, because stabilization of the developing solution and rapid processing have been greatly demanded in recent years.
In color diffusion transfer processes, a combination of an internal latent image type emulsion and hydrazines is used as one means of obtaining a direct positive image. However, this combination does not form a negative image having as high contrast as that attained in the present invention. U.S. Pat. No. 3,846,129 describes adding an aromatic alcohol dye booster to a p-phenylenediamine type viscous developing solution together with a competing developer in the color diffusion transfer process using the above-described combination of hydrazines and an internal latent image type emulsion. However, the aromatic alcohols used here are believed to have only the function of accelerating transfer of the formed dye and interaction between the alcohols and the hydrazines is not suggested at all.